The present invention relates to a method of manufacturing a semiconductor device, more particularly a device having dual gate oxides and/or a guard ring separating two active regions.
With the advances in semiconductor technology, a semiconductor device is provided increasingly with multiple functions. Such a multi-functional device is provided with different circuitries that may operate in different voltage regimes within the same chip.
In addition, as the technology advances and the devices are scaled down, the operational voltage decreases as well, particularly for high density devices. However, these high density devices, operating a low voltage, generally need to interface with other devices that may use higher Vcc. Accordingly, the high density devices are provided with an I/O circuitry to interface with the external devices having higher Vcc. For example, a high density device is provided with first circuitry configured to operate at a high voltage, e.g., about 5 volts, and second circuitry configured to operate at a low voltage, e.g., about 3.3 volts.
For optimal operation, the devices having two different voltage regimes are provided generally with dual gate oxides: a thick gate oxide configured for the high voltage and a thin gate oxide configured for the low voltage. Therefore, employing these type of combined VLSI circuits requires a technique for fabricating gate oxide layers having a significant thickness difference for diverse uses within the same silicon substrate.